Off-band Ca-H images

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thesmiths
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Off-band Ca-H images

Post by thesmiths »

Similar to a post we made recently on H-alpha viewtopic.php?t=37231, here is a mosaic made from a recent single Ca-H SHG video file. For the acquisition conditions, see this previous post viewtopic.php?t=37317.

By using the "pixel shift" feature of our software, we stepped through the Ca-H line from slightly blue (top left) to slightly red (bottom right). The mosaic below is from -10 to +10 pixels. The data is from a single SER file taken at 09:10 UTC on July 29. This is a large jpg file so best to see by opening in a new tab.

Mosaic of Ca-H SHG images, pixel shifted from -10 to +10. 2400 l/mm grating, 9 micron lithographic slit.
Mosaic of Ca-H SHG images, pixel shifted from -10 to +10. 2400 l/mm grating, 9 micron lithographic slit.
101043_CaH_shift_-10_to_10.jpg (2.77 MiB) Viewed 210 times

The centre (minimum brightness) of the Ca-H line corresponds to the central image. Each shifted image corresponds to a wavelength displacement of 7.2 picometers. The theoretical spectral resolution is about 21 picometers (0.21 angstroms). The range of wavelength shift from blue to red is a total of only 1.44 angstrom. This shows how important the proper tuning of a narrowband calcium filter is. The difference between Ca-H and Ca-K is likely not very large.

It's worth mentioning that the Doppler shift is not as visible in Ca-H as in the previous H-alpha mosaic. I think the reason is the shape of Calcium lines is much more gradual, while the H-alpha line is quite steep. This means the gradient of brightness vs wavelength is much less, so any Doppler shift does not translate into as large a shift in intensity.


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marktownley
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Re: Off-band Ca-H images

Post by marktownley »

Brilliant comparison Douglas. I know this is CaH, but is very useful to me with tuning my CaK filters.


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Re: Off-band Ca-H images

Post by thesmiths »

marktownley wrote: Fri Aug 05, 2022 7:44 am I know this is CaH, but is very useful to me with tuning my CaK filters.
I just did CaK and CaH today and the results are essentially identical. Feel free to put this one in the Solar Reference Library along with the H-alpha version.


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